1. Field of the Invention
This invention relates to a method for treating nonaqueous solvent type cells, and more particularly to a method by which component materials constituting lithium-containing cells are safely and efficiently treated and recovered for their reuse.
2. Related Background Art
Recently, in anticipation of the earth's environment becoming warmer because of the greenhouse effect etc. due to an increase in CO.sub.2, it becomes difficult to construct additional thermal power stations that discharge CO.sub.2 in a large quantity, and hence it is designed as a means for effectively utilizing electric generators, to carry out what is called load leveling, i.e., to accumulate nighttime power in secondary cells (storage cells) installed at general homes so that loads can be leveled and the power can be efficiently used. There is also an increase in demand for the development of secondary cells with a high energy density used for electric automobiles discharging no air pollution substances, and in demand for high-performance secondary cells used in power sources for portable machinery such as notebook personal computers or word processors, video cameras and portable telephones.
As the above high-performance secondary cells, rocking-chair type lithium ion cells making use of a positive electrode active material comprising lithium ions introduced as an interlayer compound and a negative electrode active material comprising carbon have gained a progress in development, and some of them are being put into practical use. Research and development are also accelerated in respect of lithium secondary cells making use of a negative electrode active material comprising metallic lithium, having a higher energy density than the lithium ion cells. In future, lithium cells are expected to be used over a wide range of from the above portable machinery power sources to electric automobiles, load conditioners and power storage.
Lithium cells making use of metallic lithium in the negative electrode, having been put into practical use as primary cells, have a very high energy density and hence have been used in large number in portable machinery such as cameras and wrist watches. They, however, are still in small number when compared with the total amount of the cells under consumption. Lithium cells formed into secondary cells can be repeatedly used and the quantity according to their use may decrease. However, with an expansion in their use as stated above, lithium-containing cells including lithium ion cells are expected to be used in an increasing amount (hereinafter, the lithium-containing cells are called lithium cells). With such an increase, the number of spent lithium cells may increase, of course.
From the standpoint of preservation of the earth's environment, resources including those in lithium cells must be recovered and reused to reduce industrial waste. [Herein, "recover" is meant to make at least part of component materials of a lithium cell into a reusable material(s)].
At present, metallic lithium that generates hydrogen upon its reaction with water and organic solvents are used in lithium cells, and there is a danger of ignition (or catching fire) when the resources constituting lithium cells are treated for their recovery. Because of use of a plurality of compounds, there is also the problem that they can not be recovered with ease. Thus, under existing circumstances, also because they are still used in a small amount, any perfect and simple method for recovering lithium cell materials and the reuse of recovered materials have not been found.
Accordingly, before lithium cells are developed, it is particularly sought to establish a method for recovering lithium cell materials in safe and in a good efficiency.